New smoke alarm tests a mother’s touch

It took over two minutes for high-pitched smoke alarms to wake kids up. It took a motherly voice just two seconds.

nikkytok/iStockphoto

This is one in a series presenting news on technology and innovation, made possible with generous support from the Lemelson Foundation.

Smoke alarms are painfully loud. They’re supposed to be, so that you can’t ignore them. Yet plenty of people — especially kids — will sleep through an alarm’s screeching noise. When the smoke is caused by fire, sleeping through that racket could prove deadly. That’s why researchers at Nationwide Children’s Hospital in Columbus, Ohio, have been testing new types of alarms that few kids sleep through. These rouse kids using their mom’s voice.

Kids who heard their mother’s voice in an alarm woke up in around two seconds. It took them only about 20 seconds more to take a pre-arranged escape route. Those who heard the standard smoke alarm often took over two minutes to rouse and nearly five minutes to escape. In a real fire, that extra time could spell the difference between life and death, the researchers say.

Sleep is a uniquely vulnerable time. Half of all fire deaths occur during the night. Knowing which alarms work best can save lives, says Mark Splaingard. He’s a doctor who took part in the new research.

One night in 1998, Splaingard treated three kids with severe burns. He was puzzled because their house had a functioning alarm, but it hadn’t woken the kids up. Within a few years, Splaingard began research to solve the problem.

First, he thought about what sounds kids might respond to most. Two possibilities stuck out: their names and their mom’s voice. People pick out their own names more easily than other sounds. Other research has shown that newborns only a day or two old can recognize their mom’s voice.

In 2006, Splaingard’s team did a small study of 24 kids. The researchers found some evidence that both a mother’s voice and the use of a first name mattered in waking kids up. But that wasn’t enough evidence to change practices. So the researchers conducted another study.

This time, the team tested 176 children between the ages of 5 and 12 at a sleep research center. All had been tested to make sure they could hear well. And before the kids went to sleep, they were taught an escape route to follow. Once the children were had fallen into a deep sleep, researchers randomly sounded a smoke alarm. The researchers noted how long it took kids to wake up, and how long they needed to follow the escape route.

Sometimes the sound was a standard, high-pitched smoke alarm. But the researchers also programmed some novel alarms with three recordings of the voice of each child’s mother. In one alarm, she repeated her child’s first name over and over. In a second, she said something like, “Wake up. Get out of bed. Leave your room.” In the last, the mother repeated her child’s name twice, then said to wake up, get out of bed and leave the room.

Standard, high-pitched smoke alarms failed to wake up 47 out of every 100 kids. Smoke alarms with a mother’s voice woke up all but 10 in every 100 kids. And it didn’t seem to matter which of the three messages a child heard. All worked equally well.

“Clearly, for kids, [standard] alarms just don’t awaken all of them,” says Splaingard. His team’s data show there can be a true risk in depending on a high-pitched alarm to rouse sleeping kids. At present, Splaingard says, “We still don’t understand the reason why kids sleep through alarms and adults don’t.”

His group published its results October 25 in the Journal of Pediatrics.

They attend to mom’s warning

Previous studies offer another possible reason for why mom’s voice works so well.

People usually speak at frequencies below 1,500 hertz (cycles per second). Most smoke alarms blare out high pitched beeps at a frequency around 3,000 hertz. Studies have shown that alarms with lower pitches — around 500 hertz, for instance — work better at waking people up. When smoke alarms were first developed, their inventors were more worried about detecting fire. They just assumed that a loud, high pitched noise would wake people up.

In fact, low frequencies would be “more effective for a whole range of vulnerable people,” says Dorothy Bruck. She’s a sleep scientist at Victoria University in Melbourne, Australia. She did not take part in the new research. People who are older, or have trouble hearing, also respond better to lower-pitched alarms, she notes.

The National Fire Protection Association now recommends using low-frequency alarms, which can be 12 times more effective. Most households, however, still rely on devices that blare out high-frequency tones.

The new study doesn’t answer whether a mother’s voice is better than a low-frequency alarm, but it does indicate that names don’t matter.

For large families, not needing to use a name could be a relief. After all, Splaingard says, “What do you do in a family that has five different kids?”

His team plans to continue testing the effectiveness of different smoke alarms. For instance, the researchers want to learn how good male voices are at waking sleeping children compared to a mother’s voice or to low-pitched alarms.

Power Words

frequency The number of times some periodic phenomenon occurs within a specified time interval. (In physics) The number of wavelengths that occurs over a particular interval of time.

hertz The frequency with which something (such as a wavelength) occurs, measured in the number of times the cycle repeats during each second of time.

pediatrics A field of medicine that has to do with children and especially child health. A doctor who works in this field is known as a pediatrician.

range The full extent or distribution of something. For instance, a plant or animal’s range is the area over which it naturally exists. (in math or for measurements) The extent to which variation in values is possible. Also, the distance within which something can be reached or perceived.

risk The chance or mathematical likelihood that some bad thing might happen. For instance, exposure to radiation poses a risk of cancer. Or the hazard — or peril — itself. (For instance: Among cancer risks that the people faced were radiation and drinking water tainted with arsenic.)

Science News for Students

Founded in 2003, Science News for Students is an award-winning online publication dedicated to providing age-appropriate, topical science news to learners, parents and educators. It’s part of the Science News Media Group, which has published its flagship magazine since 1922. SNS is a program of the Society for Science & the Public , a nonprofit 501(c)(3) membership organization dedicated to public engagement in scientific research and education. SNS — which is free to use — helps to fulfill the Society’s enduring mission to inform, educate and inspire.